1. Field of the Invention.
The present invention relates to the transfer of material from a storage location to a line operation and, more particularly, to the movement of wood chips from chip bins into the refiner line operation for making pulp.
2. Brief Description of the Prior Art.
A fundamental problem in the handling of plug flow material arises from the plug flow material's tendency to bridge and wedge and form unrelieved areas of flow so that continued flow is prevented.
In the refining of wood chips into a pulp to make paper, the quality of the pulp can be improved when the refiner operation in the paper mill is held stable, i.e., there are no flow interruptions in the lines supplying wood chips to the pulping machines or refiners.
Screw feeders are often employed for supplying the feed materials. A basic problem associated with all plug screw feeders is a tendency of chips to compact against the discharge side of the inlet hopper causing reduced bin flow, inefficient plug screw flight filling and, in some cases, complete bridging in the chip bin discharge. This bridging problem becomes more pronounced when sodium sulphite and steam are added to the chip bin because of chip swelling and softening which adversely affects chip flow characteristics. Chip flow characteristics are also reduced when chip quality, that is particle size and shape, is not closely maintained.
An axial flow pattern of chips will show compaction in the discharge area of an inlet screw feeder. Compaction is more pronounced in plug screw feeders due to a compression zone being located at the discharge side of the inlet area. As a result, there is no relieved area for the chips to flow into. Plug screw feeders with a single agitator sweep usually experience wood chip rotation above the plug screw which results in an uneven drawdown from the storage bin. The graph of screw feeding verses feed screw RPM is usually non-linear when a single agitator is used. Screw feeders heretofore have used single agitators, but these screw feeders usually had to use conventional vibrating transition pieces. These pieces are normally installed between the storage bin discharge chute and the screw feeder. However, the inlet device of the present invention does not need such a piece.
U.S. Pat. No. 4,518,262 shows a worm conveyor discharge being swept by a single agitator at the inlet end of a worm conveyor discharge. The shaft of the agitator perpendicularly crosses the axis of rotation of the screw in the worm conveyor so that material is constantly radially accelerated into the inlet end of the worm conveyor against the full end face of the screw flight.
U.S. Pat. No. 4,443,109 has a single agitator perpendicularly above the axis of rotation of a screw conveyor. The agitator vanes sweep a conical vessel above the flights of the screw conveyors but are vertically removed therefrom by the length of a cylindrical chute between the vessel and a housing for the screw conveyor.
Refiner operations not having a constant through-put rate are kept at an undesirably low level of refinement in converting wood chips into quality pulp.
In view of the above described disadvantages of the flow pattern of screw feeders heretofore know, it is the object of the present invention to provide a machine of this kind which is not subject to surges in material feed flow.